The proposed study will validate a new clinical observation instrument, the Disruptive Behavior Diagnostic Observation Schedule (DB-DOS). Recent research demonstrates that disruptive behavior problems can be broadly distinguished from normative behavior in preschoolers, based on parent interviews. The development of a standardized clinical observation method for assessing disruptive behavior in young children is a critical next step for advancing understanding of early-emerging disruptive behavior disorders because of its potential to (a) advance phenotypic description, (b) generate critical parameters for making qualitative distinctions between typical and atypical behavior during this developmental period, and (c) provide a standardized tool for integrating clinical judgment and normative developmental knowledge into diagnostic decision-making. The DB-DOS uses structured observations of the child interacting with the parent and examiner to qualitatively assess three domains hypothesized to underlie oppositional and conduct problems in young children: disruptive behavior, modulation of negative affect, and problems in competence. The principal aim of the proposed study is to establish the reliability and validity of the DB-DOS. The primary validation sample will be comprised of 360 preschoolers: 240 currently participating in the NIMH-funded Chicago Preschool Project (50% clinically referred for disruptive behavior problems and 50% demographically matched pediatric controls) and a supplementary pediatric sample of 120 non-referred children who screen high for disruptive behaviors. This enriched sample will enable the development of a DB-DOS clinical algorithm that optimizes sensitivity and specificity for identifying children along a continuum of disruptive behavior problems (both clinical cases and sub-clinical group). The psychometric properties and validity of the DB-DOS will be examined. The effects of age and sex differences, language problems, co-morbid ADHD, stressful family circumstances and observed parenting on classification will be tested. The secondary aim of the proposed project is to establish preliminary clinical utility of the DB-DOS. The reliability and validity of live clinical coding of the DB-DOS will be assessed. Validation of a standardized observational tool distinguishing between normative and disruptive behavior in preschoolers is fundamental to advancing research on the etiology, early identification and treatment of disruptive behavior disorders.